The present invention relates to pickup control devices for data reading devices. More particularly, the invention relates to a pickup control device which is suitable for either fast or slow reproduction in an optical data reading device.
In a video disk data reading system, an optical pickup is employed which applies a laser beam onto the recording surface of a disk. The laser beam reflected from or passed through the disk is demodulated in accordance with information recorded thereon. A tracking servo device is provided for a disk data reading device in such a data reading system so that the angle of rotation of the tracking mirror for deflecting the light beam is suitably controlled to cause the light beam to accurately follow the tracks on the disk at all times.
In the case where the data reading device is operated in a fast or slow reproduction mode, it is necessary for the irradiating light beam to jump recording tracks every predetermined period, for instance, every field in the case of triple speed and every two frames in the case of half speed. In a control method employed for this purpose, a jump signal is externally applied to the tracking mirror to forcibly turn the latter, and the angle of rotation of the tracking mirror is detected so that, in accordance with the detected angle of rotation, a slider is driven to control the relative position of the pickup laser beam and the disk in a radial direction. Specifically, the fact that the dc component of the mirror drive signal corresponds to the angle of rotation of the mirror is utilized to drive a slider motor.
However, if a first track being followed by the pickup is coupled through a scratch or the like to a second track to which the pickup should jump, even if the pickup jumps to the second track in response to the jump signal, it may return to the first track and, in association with this movement, the slider, motor is also returned to the former state. Thus, the pickup cannot leave the first track and hence fast or slow reproduction cannot be carried out. This phenomenon is attributed to the tracking servo control in which the slider motor is driven according to the dc signal corresponding to the angle of rotation of the tracking mirror.